The PSKDemodulator
object demodulates an input
signal using the Mary phase shift keying (MPSK) method.
To demodulate a signal that was modulated using phase shift keying:
Define and set up your PSK demodulator object. See Construction.
Call step
to demodulate the signal
according to the properties of comm.PSKDemodulator
.
The behavior of step
is specific to each object in
the toolbox.
Note:
Starting in R2016b, instead of using the 
H = comm.PSKDemodulator
creates a demodulator System object, H
.
This object demodulates the input signal using the Mary phase shift
keying (MPSK) method.
H = comm.PSKDemodulator(
creates
an MPSK demodulator object, Name
,Value
)H
, with each specified
property set to the specified value. You can specify additional namevalue
pair arguments in any order as (Name1
,Value1
,...,NameN
,ValueN
).
H = comm.PSKDemodulator(M,PHASE,
creates
an MPSK demodulator object, Name
,Value
)H
. This object has
the ModulationOrder
property set to M
,
the PhaseOffset
property set to PHASE
,
and the other specified properties set to the specified values. M
and PHASE
are
valueonly arguments. To specify a valueonly argument, you must also
specify all preceding valueonly arguments. You can specify namevalue
pair arguments in any order.

Number of points in signal constellation Specify the number of points in the signal constellation as
a positive, integer scalar value. The default is 

Phase of zeroth point of constellation Specify the phase offset of the zeroth point of the constellation,
in radians, as a real scalar value. The default is 

Output data as bits Specify whether the output consists of groups of bits or integer
symbol values. The default is 

Constellation encoding Specify how the object maps an integer or group of log2( 

Custom constellation encoding Specify a custom constellation symbol mapping vector. The default
is 

Demodulation decision method Specify the decision method the object uses as 

Source of noise variance Specify the source of the noise variance as one of 

Noise variance Specify the variance of the noise as a positive, real scalar
value. The default is 1. If this value is very small (i.e., SNR is
very high), loglikelihood ratio (LLR) computations may yield Inf
or –Inf. This result occurs because the LLR algorithm computes
the exponential of very large or very small numbers using finiteprecision
arithmetic. In such cases, use approximate LLR instead because the
algorithm for that option does not compute exponentials. This property
applies when you set the 

Data type of output Specify the output data type as When you set 
clone  Create PSK demodulator object with same property values 
constellation  Calculate or plot ideal signal constellation 
getNumInputs  Number of expected inputs to step method 
getNumOutputs  Number of outputs from step method 
isLocked  Locked status for input attributes and nontunable properties 
release  Allow property value and input characteristics changes 
step  Demodulate using Mary PSK method 
Diagrams for harddecision demodulation of BPSK signals follow.
HardDecision BPSK Demodulator Signal Diagram for Trivial Phase Offset (multiple of )
HardDecision BPSK Demodulator FloatingPoint Signal Diagram for Nontrivial Phase Offset
HardDecision BPSK Demodulator FixedPoint Signal Diagram for Nontrivial Phase Offset
Diagrams for harddecision demodulation of QPSK signals follow.
HardDecision QPSK Demodulator Signal Diagram for Trivial Phase Offset (odd multiple of )
HardDecision QPSK Demodulator FloatingPoint Signal Diagram for Nontrivial Phase Offset
HardDecision QPSK Demodulator FixedPoint Signal Diagram for Nontrivial Phase Offset
Diagrams for harddecision demodulation of higherorder (M ≥ 8) signals follow.
HardDecision 8PSK Demodulator FloatingPoint Signal Diagram
HardDecision 8PSK Demodulator FixedPoint Signal Diagram
HardDecision MPSK Demodulator (M > 8) FloatingPoint Signal Diagram for Nontrivial Phase Offset
For M > 8, in order to improve speed and
implementation costs, no derotation arithmetic is performed when PhaseOffset
is
0, $$\pi /2$$, $$\pi $$,
or $$3\pi /2$$ (i.e.,
when it is trivial).
Also, for M > 8, this block will only
support inputs of type double
and single
.
The exact LLR and approximate LLR algorithms (softdecision) are described in Phase Modulation.